From c360192bf4a8dc72f102dd6a4e1bf8bd0b404cfa Mon Sep 17 00:00:00 2001
From: Martin Schwidefsky <schwidefsky@de.ibm.com>
Date: Tue, 25 Oct 2016 12:21:44 +0200
Subject: s390/preempt: move preempt_count to the lowcore

Convert s390 to use a field in the struct lowcore for the CPU
preemption count. It is a bit cheaper to access a lowcore field
compared to a thread_info variable and it removes the depencency
on a task related structure.

bloat-o-meter on the vmlinux image for the default configuration
(CONFIG_PREEMPT_NONE=y) reports a small reduction in text size:

add/remove: 0/0 grow/shrink: 18/578 up/down: 228/-5448 (-5220)

A larger improvement is achieved with the default configuration
but with CONFIG_PREEMPT=y and CONFIG_DEBUG_PREEMPT=n:

add/remove: 2/6 grow/shrink: 59/4477 up/down: 1618/-228762 (-227144)

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---
 arch/s390/include/asm/preempt.h | 137 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 137 insertions(+)
 create mode 100644 arch/s390/include/asm/preempt.h

(limited to 'arch/s390/include/asm/preempt.h')

diff --git a/arch/s390/include/asm/preempt.h b/arch/s390/include/asm/preempt.h
new file mode 100644
index 000000000000..b0776b2c8dcf
--- /dev/null
+++ b/arch/s390/include/asm/preempt.h
@@ -0,0 +1,137 @@
+#ifndef __ASM_PREEMPT_H
+#define __ASM_PREEMPT_H
+
+#include <asm/current.h>
+#include <linux/thread_info.h>
+#include <asm/atomic_ops.h>
+
+#ifdef CONFIG_HAVE_MARCH_Z196_FEATURES
+
+#define PREEMPT_ENABLED	(0 + PREEMPT_NEED_RESCHED)
+
+static inline int preempt_count(void)
+{
+	return READ_ONCE(S390_lowcore.preempt_count) & ~PREEMPT_NEED_RESCHED;
+}
+
+static inline void preempt_count_set(int pc)
+{
+	int old, new;
+
+	do {
+		old = READ_ONCE(S390_lowcore.preempt_count);
+		new = (old & PREEMPT_NEED_RESCHED) |
+			(pc & ~PREEMPT_NEED_RESCHED);
+	} while (__atomic_cmpxchg(&S390_lowcore.preempt_count,
+				  old, new) != old);
+}
+
+#define init_task_preempt_count(p)	do { } while (0)
+
+#define init_idle_preempt_count(p, cpu)	do { \
+	S390_lowcore.preempt_count = PREEMPT_ENABLED; \
+} while (0)
+
+static inline void set_preempt_need_resched(void)
+{
+	__atomic_and(~PREEMPT_NEED_RESCHED, &S390_lowcore.preempt_count);
+}
+
+static inline void clear_preempt_need_resched(void)
+{
+	__atomic_or(PREEMPT_NEED_RESCHED, &S390_lowcore.preempt_count);
+}
+
+static inline bool test_preempt_need_resched(void)
+{
+	return !(READ_ONCE(S390_lowcore.preempt_count) & PREEMPT_NEED_RESCHED);
+}
+
+static inline void __preempt_count_add(int val)
+{
+	if (__builtin_constant_p(val) && (val >= -128) && (val <= 127))
+		__atomic_add_const(val, &S390_lowcore.preempt_count);
+	else
+		__atomic_add(val, &S390_lowcore.preempt_count);
+}
+
+static inline void __preempt_count_sub(int val)
+{
+	__preempt_count_add(-val);
+}
+
+static inline bool __preempt_count_dec_and_test(void)
+{
+	return __atomic_add(-1, &S390_lowcore.preempt_count) == 1;
+}
+
+static inline bool should_resched(int preempt_offset)
+{
+	return unlikely(READ_ONCE(S390_lowcore.preempt_count) ==
+			preempt_offset);
+}
+
+#else /* CONFIG_HAVE_MARCH_Z196_FEATURES */
+
+#define PREEMPT_ENABLED	(0)
+
+static inline int preempt_count(void)
+{
+	return READ_ONCE(S390_lowcore.preempt_count);
+}
+
+static inline void preempt_count_set(int pc)
+{
+	S390_lowcore.preempt_count = pc;
+}
+
+#define init_task_preempt_count(p)	do { } while (0)
+
+#define init_idle_preempt_count(p, cpu)	do { \
+	S390_lowcore.preempt_count = PREEMPT_ENABLED; \
+} while (0)
+
+static inline void set_preempt_need_resched(void)
+{
+}
+
+static inline void clear_preempt_need_resched(void)
+{
+}
+
+static inline bool test_preempt_need_resched(void)
+{
+	return false;
+}
+
+static inline void __preempt_count_add(int val)
+{
+	S390_lowcore.preempt_count += val;
+}
+
+static inline void __preempt_count_sub(int val)
+{
+	S390_lowcore.preempt_count -= val;
+}
+
+static inline bool __preempt_count_dec_and_test(void)
+{
+	return !--S390_lowcore.preempt_count && tif_need_resched();
+}
+
+static inline bool should_resched(int preempt_offset)
+{
+	return unlikely(preempt_count() == preempt_offset &&
+			tif_need_resched());
+}
+
+#endif /* CONFIG_HAVE_MARCH_Z196_FEATURES */
+
+#ifdef CONFIG_PREEMPT
+extern asmlinkage void preempt_schedule(void);
+#define __preempt_schedule() preempt_schedule()
+extern asmlinkage void preempt_schedule_notrace(void);
+#define __preempt_schedule_notrace() preempt_schedule_notrace()
+#endif /* CONFIG_PREEMPT */
+
+#endif /* __ASM_PREEMPT_H */
-- 
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